This invention relates, in general, to mechanical circulatory support systems and methods for their use. Various aspects of the invention relate to methods of detecting and mitigating ventricular suction events.
Suction detection and prevention is critical for heart failure patients supported by blood pumps (e.g. a ventricular assist device or VAD). In the case of a VAD, a suction event refers to an instance of negative pressure created in the ventricle. A suction event, which is typically triggered by a pump speed too high for the given systemic conditions and a patient's physiology, affects clinical outcomes and can lead to major adverse events in extreme cases. Suction events can be avoided by lowering the pump speed when such an event is detected. A speed reduction may not completely prevent suction, but it will reduce the likelihood of a continuous severe suction condition under normal pump operation.
One typical method for detecting a suction event includes the trend analysis of a pulsatility index (PI). PI is a measure of the variability of blood velocity in a vessel, and in the case of a VAD, PI is a measure of the pressure differential inside the VAD pump during the native heart's cardiac cycle and represents volume status, right ventricle function, and native heart contractility. PI may be calculated taking into consideration factors such as pump power, current, back electromotive force (emf). Another method for detecting a suction event includes correlating the pump flow waveform to a database of signals indicating suction events. Yet another method includes performing a harmonic analysis of the pump power or pump flow waveform. Exemplars of existing suction detection techniques are described in U.S. Pat. No. 7,645,225 to Medvedev, U.S. Pat. No. 7,175,588 to Morello, U.S. Pat. No. 6,991,595 to Burke et al., and U.S. Pat. No. 5,888,242 to Antaki et al. and U.S. Pub. No. 2014/0100413 to Casas, which are incorporated herein for all purposes by reference.
Existing methods for detecting the imminence or presence of a suction event have several limitations.
Methods other than waveform correlation are limited in their capability to discern a suction event when compared to other patient physiological conditions that may not have any relevance to a suction condition (U.S. Pub. No. 2014/0100413 to Casas). Accordingly, the results can be inaccurate and lead to false positive detection of a suction event. Although waveform correlation methods can be more accurate, these techniques are challenging to implement because they require a database of suction event signals against the input signal be matched (U.S. Pat. No. 7,175,588 to Morello). The correlation of signals also requires extensive signal processing capabilities. Such capabilities are typically not available in embedded systems used to drive LVAD pumps. Extensive signal processing also tends to lead to greater energy usage and heat which can be challenging when the components are implanted in the body or directly against the skin.
What is needed are devices and methods which overcome the above disadvantages. What is needed is an improved suction detection technique.